Gd-DOTA, a potential MRI contrast agent. Current status of physicochemical knowledge.

The complex (Gd-DOTA) meglumine has recently been used as an MRI contrast agent in humans. Due to its particularly interesting physicochemical properties, the risk of in vivo dissociation of the complex is reduced. Indeed, as a result of the macrocyclic nature of the DOTA ligand, Gd-DOTA appears very stable, demonstrating a calculated conditional stability constant of 10(22.19) at pH = 7. Other characteristics making Gd-DOTA a positively attractive compound include slow dissociation kinetics inherent in the rigidity of the macrocycle and marked specific affinity of DOTA for gadolinium in comparison with other endogenous ions. Finally, although the relaxivity R1 of Gd-DOTA at 20 MHz appears similar to that of Gd-DTPA, Gd-DOTA demonstrates higher paramagnetic efficacy at low field strength due to greater symmetry of the complex. Such promising properties open up wide prospects for the use of Gd-DOTA in MRI.